The Controversial Origin of Central Utah’s

Geologic Complexities 

By Irving J. Witkind

U.S. Geological Survey Bulletin 2166

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

Bruce Babbitt, Secretary

U.S. Geological Survey

Charles G. Groat, Director

Any use of trade, product, or firm names is for

descriptive purposes only and does not imply 

endorsement by the U.S. Government

Published in the Central Region, Denver, Colorado

Manuscript approved for publication February 3, 1999

Graphics by David G. Walters and Norma J. Maes

Photocomposition by Norma Maes and Lorna Carter

Edited by Lorna Carter

This report is only available on-line at:

http://greenwood.cr.usgs.gov/pub/bulletins/b2166/index.html
III

CONTENTS

Introduction .................................................................................................................... 1

Central Utah’s Structural Setting............................................................................ 1

Physiography .................................................................................................. 1

Wasatch Plateau .................................................................................... 1

The Sanpete–Sevier Valley Area .......................................................... 3

Stratigraphy .................................................................................................... 3

The Diapiric Concept...................................................................................................... 3

The Arapien Shale .................................................................................................. 3

Salt.......................................................................................................................... 3

Salt Diapirics .......................................................................................................... 3

Rate of Salt Movement................................................................................... 5

Slow Upward Movement ...................................................................... 5

Rapid, Upward Surges .......................................................................... 5

Diapiric Structures in Central Utah ................................................................................ 5

Minor Structures..................................................................................................... 5

Thistle Area (A-4) .......................................................................................... 7

Sterling Area (G-3)......................................................................................... 7

Major Structures ..................................................................................................... 7

Development of Major Diapiric Folds............................................................ 7

Episodes ................................................................................................ 7

Stages .................................................................................................... 7

Monoclines ..................................................................................................................... 7

The Valley Mountains Monocline (G-2) ................................................................ 10

Conclusions .................................................................................................................... 10

References Cited............................................................................................................. 11

FIGURES

1. Index map of central Utah ........................................................................................................................................... 2

2. Cross section through a diapiric fold........................................................................................................................... 3

3. Sketches suggesting how a diapiric fold may form and then fail................................................................................ 5

4. Sketches showing difference between a static hill and a dynamic upwarp................................................................. 6

5. Sketches showing fundamental difference between an anticline and a diapiric fold .................................................. 8

6. Photographs showing salt-rich Arapien Shale intruding and deforming country rocks, U.S. Highway 6 between

 Price and Provo, Utah.................................................................................................................................................. 9

7. Map showing Sterling area.......................................................................................................................................... 10

8. Diagrammatic sketches illustrating how sequence of intrusion, erosion, and deposition deformed rocks exposed

in Red Rocks area........................................................................................................................................................ 12

9. Cross sections showing fundamental differences between a typical Colorado Plateau-type monocline and a

 similar-appearing central Utah monocline .................................................................................................................. 14

10. Sketches of Red Canyon area, Valley Mountains ....................................................................................................... 15

TABLE

1. Some stratigraphic units exposed in central Utah ....................................................................................................... 4
1

The Controversial Origin of Central Utah’s

Geologic Complexities

By Irving J. Witkind

Introduction

Geology, a somewhat inexact science, differs from the 

more precise sciences such as chemistry and physics. In 

geology, many complex rock exposures are not readily decipherable, and consequently lend themselves to differing 

interpretations. Geologists have a wry jest: one outcrop, two 

geologists, three interpretations! Regrettably, the enigmatic 

exposures in central Utah invite such unbridled speculation. 

Despite the hordes of geologists who have swarmed over 

central Utah during the past half century, no firm consensus 

has been reached concerning central Utah’s tangled geologic 

history. Contending geologists, in hot debate, have commonly offered two dramatically different interpretations.

One interpretation, proposed more than half a century 

ago, suggests that mountain-building forces—commonly 

referred to as tectonic forces—coming from the west repeatedly deformed central Utah. This interpretation, here termed 

the multiple-tectonic concept, is favored by many geologists 

(DeCelles and others, 1995; Lawton, 1985; Standlee, 1982). 

A second interpretation, relatively new, proposes that the 

structural deformation in central Utah is best explained as 

the result of the repeated growth and collapse of large salt 

masses known as salt diapirs—the salt-diapiric concept 

(Witkind, 1983; 1987; 1994).

I contend that the contained salt in the Arapien 

Shale—expressed as salt diapirs—is the driving force that 

complexly deformed the rocks in central Utah. If valid, this 

view could have great economic significance. Elsewhere, 

throughout the United States and the world, large petroleum 

deposits are concentrated near salt diapirs comparable to 

those found in central Utah. One need look no farther than 

the Paradox Basin in southeastern Utah and southwestern 

Colorado to see a convincing relationship between salt diapirs and petroleum.

This article describes only the rudimentary features

of the salt-diapiric concept. Additional details are available 

in U.S. Geological Survey Professional Paper 1528 (Witkind, 1994). Those readers interested in particulars of the 

multiple-tectonic concept should contact Douglas A. 

Sprinkel, Utah Geological Survey, P.O. Box 146100, Salt 

Lake City, Utah 84114-6100. Sprinkel’s telephone number 

is: 801-537-3316; his e-mail address is: 

sprinkel@mail.vii.com.

The U.S. Geological Survey and the Utah Geological 

Survey, both sponsors of geologic studies in central Utah, 

take no official stance favoring either concept.

Central Utah’s Structural Setting

Physiography

Figure 1 covers that part of central Utah wherein crop 

out many of the complex geologic features that have so 

intrigued geologists. I arbitrarily divide this sector into two 

parts: the huge mass of the Wasatch Plateau on the east 

(essentially that part of the area east of U.S. Highway 89), 

and the remainder of the area, to which I apply the wellestablished name “Sanpete–Sevier Valley area.” Part of the 

region discussed here, chiefly the western sector, extends 

slightly beyond the normally accepted limits of the 

Sanpete–Sevier Valley area, but for ease of discussion I continue to use that name.

For ease of referring from text to figure 1, locality 

names in the text are followed by a letter and numeral,

thus, Mayfield (G-3). The letter-numeral combination 

locates the feature via the grid overlaid on figure 1.

Wasatch Plateau

The Wasatch Plateau, the northernmost of the high plateaus of Utah, is a flat-topped mass about 80 miles long and 

some 40 miles wide that extends from Salina Creek Canyon 

on the south to the valleys of Soldier Creek and Price River 

on the north (all three localities are east of the area of figure 

1). The plateau trends about N. 20o E., and maintains a constant altitude of about 10,000 feet. It separates Sanpete Valley (F-3) on the west from Castle Valley (east of the area of 

fig. 1) on the east. The plateau is underlain by nearhorizontal Cretaceous and Tertiary strata, which flex down 
2 THE CONTROVERSIAL ORIGIN OF CENTRAL UTAH’S GEOLOGIC COMPLEXITIES

Sevier 

River

Sevier

Bridge

Reservoir

Sixmile Creek

Ninemile Reservoir

Gunnison 

Reservoir

Joes Valley

Reservoir

Great

Salt Lake

Green 

River

Sevier River

Colorado

River

Provo Salt Lake City

Ogden

Nephi Price

Richfield

Cedar

City Paradox 

Basin

Area of 

enlarged

index map

Logan

Salina

Sigurd

Redmond

Gunnison

Mayfield

Manti

Ephraim

Wales

Moroni

Spring City

Mt Pleasant

Fountain Green Fairview

Indianola

Thistle Santaquin

Nephi

Levan

WASATCH PLATEAU

WASATCH MONOCLINE

SAN PITCH MOUNTAINS

(GUNNISON PLATEAU)

SANPETE VALLEY

Sterling

Red

Canyon

VALLEY

MOUNTAINS

VALLEY

MOUNTAINS

MONOCLINE

ARAPIEN VALLEY

Red 

Rocks

28

132

89

50

89

89

6

6

0 10 20 30 KILOMETERS

0 10 20 MILES

 114°

38°30′

45′

39° 00′

15′

30′

45′

40°00′ 112°00′ 45′ 30′ 15′

112°

110° 41°

39°

37°

WASATCH RANGE

CEDAR HILLS

SEVIER PLATEAU

YUBA 

DAM

SANPETE-SEVIER VALLEY AREA

1 2 3 4 5

WESTERN PART

OF WASATCH

PLATEAU

A

B

C

D

E

F

G

H

I

J

K

15

15

70

70

Richfield

0 100

0 50

200 KILOMETERS

100 MILES

Figure 1. Index map of central Utah. A letter and numeral identify all localities mentioned in text, for example, Sterling (G-3). 

These letter-numeral combinations are 

keyed to this illustration.
THE DIAPIRIC CONCEPT 3

along the west flank of the plateau to form the imposing 

Wasatch Monocline (F-4), some 62 miles long. High-angle 

normal faults, trending both north and about N. 20o E., break 

much of the plateau and the monocline. Locally these faults 

are paired to form grabens (elongate, narrow troughs 

bounded by near-parallel normal faults).

The Sanpete–Sevier Valley Area

The name, Sanpete–Sevier Valley area, used repeatedly 

in the geologic literature, encompasses an irregular area centered about the San Pitch Mountains, also known as the 

“Gunnison Plateau” (E-3). The Sanpete–Sevier Valley area 

is an arid lowland broken here and there by north-trending 

plateaus and low hills considerably lower than the adjacent 

Wasatch Plateau. Sedimentary, metamorphic, and volcanic 

rocks, more or less deformed, underlie most of these 

uplands. The very western part of the Sanpete–Sevier Valley 

area (as used here) includes the eastern reaches of the Basin 

and Range province.

Stratigraphy

Table 1 lists many (but not all) of the sedimentary units 

exposed in this sector of central Utah. Of all formations 

listed, the Arapien Shale of Middle Jurassic age, a unit rich 

in evaporites such as salt and gypsum, has played the greatest role in structurally deforming central Utah. I discuss the 

characteristics of the Arapien Shale later in this report.

The Diapiric Concept

In brief, the upward thrust of a rising salt diapir forces 

up the enveloping mudstones, and they, in turn, push up and 

locally overturn the overlying sedimentary strata to form a 

major upwarp—a salt-cored anticline, or diapiric fold, as 

these upwarps are sometimes called (fig. 2).

Although ample evidence of salt movement in the geologic past is widespread throughout central Utah, some tenuous evidence, in the form of recently tilted sedimentary 

deposits, supports the view that the salt is still moving today 

and still deforming the bedrock upon which humans have 

constructed many of their buildings. I can only conclude that 

the salt diapirs are contemporary geologic hazards.

The Arapien Shale

Vast amounts of salt and other evaporites, such as gypsum and anhydrite, are integral parts of the Arapien Shale, 

one of the most unusual formations in Utah. The Arapien, 

named for its excellent exposures in Arapien Valley (H-3) 

near Mayfield, Utah (G-3), has many appearances. Commonly it is a light-gray, almost white mudstone mottled here 

and there with pink blotches. This blotched appearance is 

distinctive and characterizes most Arapien exposures; it is 

best seen in the broad expanses between Salina (I-2) and 

Richfield (J-1), especially east of Sigurd (I-2). In places, 

however, the Arapien is red, bluish gray, and dark gray.

Salt

What makes the Arapien so unusual is its enormous 

content of evaporites, chiefly salt and gypsum. Salt is mined 

at Redmond (H-2), and gypsum near Sigurd (I-2), Salina (I2), and Nephi (C-2). Both minerals contribute to the economic wealth of central Utah.

Salt is easily dissolved in the temperate climate that 

characterizes the Western Interior of the United States. No 

sooner does the salt reach the surface than it passes into solution. As a result it is seldom exposed. Thus, in the Paradox 

Basin, underlain by extensive deposits of salt, none is 

exposed at the surface. Central Utah, also underlain by much 

salt, displays only small amounts at the surface, chiefly near 

Salina (I-2) and Redmond (H-2).

Salt Diapirs

Salt is a remarkably mobile material. Deposited in horizontal beds, in many places it begins to move both laterally 

and vertically shortly after deposition. Why it starts moving 

2 KILOMETERS

1 MILE

0 

0 

1 

Salt diapir

"Mother bed of salt" "Mother bed of salt" 

Deformed

country rocks

Deformed

country rocks Diapiric sheath

of crumpled

mudstone

Diapiric sheath

of crumpled

mudstone

Diapiric fold

Figure 2. Cross section through a diapiric fold (salt-cored anticline). Arrows indicate general direction of movement of the mobile, plastic salt and mudstone. In places, upward vertical forces, 

stemming from the intrusive salt diapir, are translated laterally into 

horizontal compressive forces. Scale is approximate.
4 THE CONTROVERSIAL ORIGIN OF CENTRAL UTAH’S GEOLOGIC COMPLEXITIES

System Series Group and formation Symbol Thickness

(feet) Lithology

Tertiary Eocene

Paleocene

Green River Formation Tg

Tu 

TKu 

KJu 

Tc

1,200

Colton Formation 450–600

Flagstaff Limestone Tf 50–1,800

Upper

Cretaceous

North Horn Formation Tkn

Kpr

Kl

Kcm

150–3,000

Price River Formation 20–2,000

3,000–7,000

300–2,000

3,000

4,000–13,000

320–450

500–1,000

300–1,000

400–1,000

11,500

Jtg

Ja

Jtc

Jn

Pu

u

u

Indianola Group

Cedar Mountain Formation

Twist Gulch Formation

Arapien Shale

Members of the

Twin Creek Limestone

Navajo Sandstone

(Nugget Sandstone)

Triassic strata, undivided

Permian strata, undivided

Pennsylvanian strata, 

undivided

Lower

Cretaceous

Middle

Jurassic

Lower 

Jurassic

Upper to Lower

Triassic

Lower Permian

Upper to Lower

Pennsylvanian

Cretaceous

Jurassic

Triassic

Permian

Pennsylvanian

Limestone underlain by shale unit

Claystone and mudstone

Limestone with subordinate shale

Mudstone, sandstone, conglomeratic 

sandstone

Conglomerate, conglomeratic 

sandstone, siltstone

Conglomerate, conglomeratic sandstone, 

sandstone

Shaly siltstone and mudstone,

some limestone

Shaly siltstone and sandstone

Calcareous mudstone, much salt and

other evaporites

Limestone, thin-bedded to massive

Sandstone, light-brown

Chiefly shale, siltstone, some limestone

Limestone, cherty limestone

Interbedded limestone and sandstone

Table 1. Some stratigraphic units exposed in central Utah.

[Tu, Tku, and so on are symbols for combined units]

is unknown; several explanations have been proposed. One 

of the more reasonable suggestions attributes this initial 

movement to the reactivation of a nearby existing fault. In 

time, lateral migration leads to the development of large salt 

masses.

Because the specific gravity of salt is less than that of 

the surrounding sedimentary rocks, the buoyancy of the salt 

causes these large salt masses to rise. In their upward ascent, 

they push up and fold back the overlying strata, and then 

punch through them in a process called piercement. Piercement characterizes most diapirs, the name geologists apply to 

these rising salt masses.

Some of these diapirs are round, even as others are linear and ridgelike. Along the coastal plains of Texas, Louisiana, and Mississippi, many of the diapirs are rounded salt 

masses with near-vertical walls. Elsewhere, as, for example, 

in northern Germany, the diapirs are thin, narrow, ridgelike 

salt bodies that extend for miles.

Ridgelike diapirs characterize the Arapien Basin in central Utah as well as the Paradox Basin.

As the salt core of a ridgelike diapiric fold begins to dissolve in the subsurface, the crestal part of the fold either subsides between boundary faults or sinks into the newly formed 

voids (fig. 3B). Erosion quickly destroys the foundered remnants. The upturned limbs of the fold, lacking support, fail 

and sag to form paired, facing monoclines (fig. 3C).

Intermittently and repeatedly during the past 175 million years, the rising salt forced up the overlying, younger 

sedimentary strata to form these giant salt-cored upwarps 

that dominated the area. Each time, as the salt core dissolved, these upwarps collapsed. Erosion then reduced the 

remnants, leaving only steeply tilted or overturned beds here 

and there as evidence of their former presence. An 

outstanding example of such a remnant is the vertical ridge 

that defines much of the east flank of the Gunnison Plateau 

(San Pitch Mountains (E-3)). The ridge is readily examined 

near Wales (E-3).
DIAPIRIC STRUCTURES IN CENTRAL UTAH 5

Country rocks Country rocks

Tu

Tu

Tu

Tu

Tu

Tu

Arapien Shale

Ja

Tku

Kju

Tu

Tku

Kju

A

Ground surface

Tu Tu

Country rocks Country rocks

Arapien Shale

Tku

Tu

Tu Tu

Ja

Tku

Kju Kju

B

Ground

surface

Ground

Alluvium surface

Tu

Kju

Paired, facing

monoclines

Ja

Shale

Ja

Kju Arapien

Tu

Tku Tku

C

Rate of Salt Movement

The salt moved at different rates as it rose toward the 

surface. For much of the time its rate of upward movement 

was almost imperceptible. Every now and then, however, it 

seems to have surged upward rapidly, almost spasmodically.

Slow, Upward Movement

Entire sequences of geologic formations—not just one 

or two formations—are both bowed up and anomalously thin 

near these salt-cored upwarps, implying that the implacable 

upward thrust of the rising salt forced these salt-cored anticlines upward slowly but continuously. Expectably, the rate 

of the rising salt determined the rate of the upward movement of the upwarp. These upwarps, thus, are best viewed 

as dynamic, moving masses, rather than static, stationary 

ones. If sediments were burying a static hill, several formations would thin, reflecting where those sediments were 

deposited against its flanks. Once the static hill was buried, 

younger formations would pass over it unchanged in thickness (sketches in A, fig. 4).

Rapid, Upward Surges

Brief but pronounced upward surges of the salt interrupted these lengthy episodes during which the salt rose 

slowly. Seemingly, at these times the salt surged upward in 

sudden spasmodic movements to form the enormous, linear 

diapiric folds. These salt-cored upwarps have been called 

anticlines, salt-cored anticlines, and diapiric folds. Figure 5 

illustrates the difference between the terms, and why the 

term “anticline” may be misleading.

The descriptive term is important. If, as I contend, 

upward movement of Arapien salt is responsible for the 

development of the complex structures that characterize 

central Utah, these structures should extend down to the 

base of the salt-bearing Arapien Shale, but no deeper. 

Older formations below the Arapien may also be deformed, 

but if so, they were deformed by tectonic forces, not salt 

movement. In economic terms, then, two types of petroleum 

reservoirs may underlie central Utah—near-surface ones 

developed in the salt-generated structures, and deeper ones 

in the folded units concealed beneath the Arapien Shale.

Diapiric Structures in

Central Utah

The diapiric structures found throughout central Utah 

include minor ones that are readily examined in the field, as 

well as major structures that extend for tens of miles and that 

are more difficult to perceive because of their great size and 

the extensive erosion they have undergone. 

Figure 3. Several sketches suggesting how a diapiric fold may 

form and then fail. A, The rising salt diapir (not shown but within 

the Arapien Shale (Ja)) forces up the surrounding mudstones, 

which, in turn, push up and fold back the overlying country 

rocks. B, As the diapiric salt core gradually dissolves, support 

for the overlying strata is removed. The crest of the fold 

founders, breaking into large masses. Erosion attacks the failed 

fold. C, Erosion quickly destroys these fragmented blocks. 

Continued removal of salt from the salt core, and the resulting 

subsidence, culminates in downward flexing of both of the upwarp’s flanks to form paired, facing monoclines.

Minor Structures

I discuss here only two of the many minor salt-derived 

structures found in central Utah, one in the Thistle area (A4), and another in the Sterling area (G-3).
6 THE CONTROVERSIAL ORIGIN OF CENTRAL UTAH’S GEOLOGIC COMPLEXITIES

B

Arapien Shale

Arapien Shale

a

b

c

a

b

c

Arapien Shale

a

b

c

d

a

b

c

d

Hill

Partly buried hill

a

b

c

a

b

c

Completely buried hill

a

b

c

d

e

f

a

b

c

d

e

f

A

I I 

II II 

III III 

Figure 4. The critical difference between a static hill and a dynamic upwarp. A, Static hill. Sediments deposited against a static hill thin 

where they abut the flanks of the hill (units a, b, and c of sketch II). Once the hill has been buried they pass over it unchanged in thickness 

(units d, e, and f of sketch III). B, Dynamic upwarp. The dynamic upwarp (sketch I), driven by the rising salt (not shown), continues to rise 

as long as the salt maintains its upward movement (sketch II). Two characteristics mark this upward movement (sketches II and III): (1) 

The strata are warped up along the flanks of the rising mass; and (2) all strata along the upwarp’s flanks thin anomalously.
MONOCLINES 7

Thistle Area (A-4)

Shortly after the disastrous Thistle Landslide of 1983, 

which effectively blocked the major highway (U.S. 6) connecting Price and Provo (small index map, fig. 1), construction crews cut a new highway through a ridge north of the 

landslide. The new roadcut exposes masses of Arapien 

Shale that intrude beds of the Twin Creek Limestone that 

form the ridge. Photographs of these exposures demonstrate 

not only the different aspects of the Arapien but also its 

intrusive nature (fig. 6).

Sterling Area (G-3)

The intrusive and deforming aspects of the Arapien 

Shale show well directly south of Sterling (G-3) near Ninemile Reservoir (G-3). In that area, the Green River Formation (the formation, incidentally, that furnished the limestone 

blocks used to construct the magnificent Mormon Temple at 

Manti (F-4)) forms a narrow, north-trending sag (syncline) 

followed by Arapien Valley (H-3). In detail, Green River 

strata east of Arapien Valley dip west as part of the Wasatch 

Monocline (F-4) (fig. 7). West of Arapien Valley (H-3), 

these same strata, exposed along the east flank of a small, 

unnamed knoll, are unexpectedly inclined to the east! Why 

the abrupt change in dip? The geologic relations displayed 

along the west flank of this unnamed knoll explain this surprising change. The exposures indicate that the Arapien 

Shale intruded and pushed up the overlying Green River 

beds and in so doing inclined them to the east.

Major Structures

The major, elongate, diapiric folds trend generally 

north or slightly east of north. At least 13 of these major diapiric folds, all deeply eroded, have shaped the landscape of 

central Utah.

Development of Major Diapiric Folds

Episodes

The salt diapirs surged upward at least three and possibly four times, and each time they warped the overlying 

strata into the elongate diapiric folds. The first episode 

likely began about 65 million years ago. A second probably 

started some 60 million years ago, and a third about 22 million years ago. Some evidence suggests that a fourth episode 

occurred about 25,000 years ago. The tilting of some modern sedimentary deposits implies that the salt is still active 

today. I am uncertain how long each of these episodes 

lasted.

Stages

Each diapiric episode logically divides into three 

stages—an intrusive stage, an erosional stage, and finally, 

a depositional stage. Figure 8 illustrates the interrelations of 

these three stages, and how they characterize each diapiric 

episode.

During the intrusive stage, the salt surges upward to 

form a salt-cored diapiric fold (III, fig. 8). Subsequently, as 

dissolution destroys the salt core, the fold collapses (IV, fig. 

8), and the erosional stage begins, eventually forming a surface of low relief (V, fig. 8). Sediments deposited on this 

newly formed surface (VI, fig. 8) mark the beginning of the 

depositional stage. A renewed upward surge of the salt (VII, 

fig. 8)—the intrusive stage of the next diapiric episode—ends the depositional stage. These same three stages 

are repeated during each diapiric episode, and this repetition, 

time and time again, has determined the structural pattern of 

central Utah.

The geologic evidence suggests that each time the new 

diapiric folds formed they occupied the same sites and had 

the same trends as the previous, older diapiric folds. This 

implies that during the intrusive phase of each new episode, 

the remobilized salt surged up the same conduits previously 

followed by the earlier upward surges of the salt.

One possible explanation for this repeated use of the 

same conduits by the rising salt involves recurrent reactivation of the same major, ancient faults. Each time the faults 

moved, they triggered renewed movement of the salt. 

Expectably, the upward surge of the salt pushed up the surrounding mudstones, and these, following the established 

fault planes, forced up the overlying sedimentary rocks to 

form new diapiric folds whose trends coincided with the 

trends of former diapiric folds long since eroded and partly 

destroyed.

Monoclines

The paired, facing monoclines that formed when a diapiric fold failed (fig. 3C) are most unusual and not at all like 

those monoclines found elsewhere throughout the Colorado 

Plateau. Figure 9 illustrates the critical differences between 

the Colorado Plateau-type monoclines and those in central 

Utah. The east-facing Valley Mountains monocline (G-2) 
8 THE CONTROVERSIAL ORIGIN OF CENTRAL UTAH’S GEOLOGIC COMPLEXITIES

Tg

Tc

Tf

TKn

Kpr

Ki

Kcm

West East

A

  yyy yyy

Kcm

Jtg

Jtc Jtc

Jn Jtc

Jn

Jn

Jn

Jtc

Kcm

Jtg

Mudstones of the Arapien Shale Mudstones of

the Arapien Shale

Ja

Ja

Ja

Ja

West East

Ja

Ja 

C

u

u

?

?

Arapien

Shale

Arapien

Shale

SALT

  yyy yyy Kcm Kcm

Jtg

Jtg

Mudstones of the Arapien Shale

Mudstones

of

the Arapien Shale Ja Ja

Jn

Jn

Jtc Jtc

Ja Ja

Jtc

Jtc

?

?

B 

u

u

Arapien

Shale

Arapien

Shale

SALT

Tg

Tc Eocene

Paleocene

Upper

Cretaceous

Lower

Cretaceous

Middle

Jurassic

Lower

Jurassic

Thrust fault—Dashed where 

 approximately located; queried

 where uncertain

Triassic,

undivided

EXPLANATION

TERTIARY

CRETACEOUS

JURASSIC

TRIASSIC

Green River Formation

Tf

Colton Formation

TKn

Flagstaff Limestone

Kpr

North Horn Formation

Kl

Price River Formation

Kcm

Indianola Group

Jtg

Cedar Mountain 

Formation

Ja

Twist Gulch Formation

Jtc

Arapien Shale

Jn

Twin Creek Limestone

Navajo Sandstone

Triassic strata, undivided

u

Figure 5 . Sketches showing the fundamental difference between an anticline and a diapiric fold (salt-cored anticline). A, 

Section across a simple anticline. All strata are flexed into an upwarp. The units are much like the layers of an onion—the underlying formations conform closely to the overlying ones. B, Section 

across a diapiric fold (salt-cored anticline). The formations are divisible into two groups: an upper group consisting of the salt-bearing Arapien Shale (Ja) and the overlying younger units (units Jtg 

and Kcm in these sketches), and a lower group that underlies the 

Arapien Shale (Ja), (units Tru, Jn, and Jtc). C, The Arapien mudstones (Ja), forced upward by the rising salt, have warped the upper group of beds (units Jtg and Kcm) into a diapiric fold (saltcored anticline). The lower group of strata (Tru, Jn, and Jtc) are 

deformed, but this deformation is unrelated to the movement of the 

salt and likely results from eastward-directed mountain-building 

forces.
MONOCLINES 9

Figure 6. New U.S. Highway 6 through a ridge composed of Twin Creek Limestone beds 

(Jtc) of Middle Jurassic age. Exposures demonstrate that the salt-rich Arapien Shale (Ja) 

locally intrudes and deforms the country rocks. A, The Arapien Shale (Ja) intrudes and deforms tilted beds of the Twin Creek Limestone (Jtc). B, A dike-like, intrusive mass of the 

Arapien Shale (Ja) separates the Twin Creek Limestone (Jtc) and the Colton Formation (Tc) 

of Eocene age.

Jtc Ja Tc

Twin Creek

Limestone

Colton

Formation

Arapien

Shale

B

EAST WEST

Jtc

A

Jtc Jtc

Ja

WEST EAST

Ja
10 THE CONTROVERSIAL ORIGIN OF CENTRAL UTAH’S GEOLOGIC COMPLEXITIES

SANPETE VALLEY

Ja

Ja

Tg

Tg

Ja

Qsw

Qsw

WEST EAST

Tu-KJu

Qal

Ja

Qsw

TgWASATCH MONOCLINE

Tg

Arapien Valley

WASATCH

MONOCLINE

Ja

65

30

10

10 20

65

45

60 20

10

Qsw

Tg

Ja

Qsw

Ja Ja 

Tg Qsw

Tg

 Tu-KJu 

West East 

 Feet 

WASATCH MONOCLINE

Arapien Valley

Unnamed knoll

Sanpete Valley

6,000

5,000

Qsw

Qsw 

Twelvemile

Creek

San Pitch

River

Ninemile

Reservoir

A A′

A A′

Vertical scale exaggerated 2x

Unnamed knoll

0.5

0.5

0 2 KILOMETERS

0

1

1 MILES

Figure 7 (above and following page). The Sterling area. Green 

River strata (Tg), inclined to the west as part of the Wasatch Monocline, pass below and are concealed beneath the floor of Arapien 

Valley (cross section A–A’). When they reappear (as part of a 

small unnamed knoll) along the west edge of the valley, they have 

reversed dip and are inclined eastward—a surprising change. 

What caused the unexpected reversal in dip? The west flank of 

the small, unnamed knoll contains the answer. The Arapien Shale 

(Ja), exposed there, pushed up the former westward-inclined 

Green River beds (Tg), forcing them into an eastward dip (cross 

section A–A’, arrow). Explanation on next page.

displays well the unusual structural relations that characterize the central Utah monoclines.

The Valley Mountains

Monocline (G-2)

The Valley Mountains monocline (G-2) extends for 

about 28 miles along the east flank of the Valley Mountains 

(G-1). The monocline for the most part is undissected (much 

like fig. 9B). Only near its north end, near Yuba Dam (E-1), 

is the monocline breached for about 5 miles; the downwarped Flagstaff limestones that define the monoclinal slope 

(Tf, fig. 10, which is a diagrammatic sketch of the south wall 

of Red Canyon (F-1) in the Valley Mountains) have been 

eroded exposing the underlying strata (Kpr-TKn and KJu, 

fig. 10).

These strata, rather than conforming in attitude to the

downwarped Flagstaff limestone beds (Tf) that form the

surface units, are near-vertical and locally overturned. In

addition, they are anomalously thin.

This structural pattern—upturned, anomalously thin 

older rocks (units KJu and Kpr-TKn, sketch I, fig. 10), overlain by downturned, anomalously thin younger ones (unit 

Tf)—has also been found near the mouth of Sixmile Canyon 

where Sixmile Creek (G-4) cuts through the Wasatch Monocline (F-4). Geophysicists have also recognized the same 

pattern in the subsurface of central Utah.

Such structural relations, I contend, are reasonably 

explained only by invoking multiple episodes of salt diapirism. Figure 10 demonstrates how a sequence of multiple diapiric events can result in upturned older beds overlain by 

downturned younger ones.

Conclusions

Right now, and with our current state of knowledge, 

no one can state with absolute certainty that any one concept explains central Utah’s geologic complexity. It is my 

firm belief, however, that when we eventually resolve this 

vexatious dilemma, we will find that multiple episodes of 

salt diapirism played a major role in deforming the strata in 

central Utah.
REFERENCES CITED 11

 

Contact—Approximately located or inferred

Arapien Shale

Older strata

Green River Formation

Alluvium Slope wash

and

valley fill

20

65

Middle Jurassic

EXPLANATION

Eocene

QUATERNARY

TERTIARY

CRETACEOUS AND

JURASSIC

Holocene and

Pleistocene

Paleocene and

Cretaceous

Includes units of: Colton Formation 

 (Eocene); Flagstaff Limestone (Paleo-

 cene–Eocene); North Horn Formation 

 (Paleocene–Upper Cretaceous); Price

 River Formation (Upper Cretaceous);

 Indianola Group (Upper Cretaceous):

 and Cedar Mountain Formation (Lower

 Cretaceous)

Attitude (strike and dip) of

 Inclined beds

 Overturned beds

 

Tg

Tu-KJu

Ja

Qal Qsw

Sequence of deposition

References Cited

DeCelles, P.G., Lawton, T.F., and Mitra, G., 1995, Thrust timing, 

growth of structural culminations, and synorogenic sedimentation in the Sevier orogenic belt, western United States: Geology, v. 23, no. 8, p. 699–702.

Lawton, T.F., 1985, Style and timing of frontal structures, central 

Utah: American Association of Petroleum Geologists Bulletin, 

v. 69, no. 7, p. 1145–1159.

Standlee, L.A., 1982, Structure and stratigraphy of Jurassic rocks in 

central Utah; their influence on tectonic development of the 

Cordilleran foreland thrust belt, in Powers, R.B., ed., Geologic 

studies of the Cordilleran thrust belt: Rocky Mountain Association of Geologists, p. 357–382.

Witkind, I.J., 1983, Overthrusts and salt diapirs, central Utah, in

Miller, D.M., Todd, V.R., and Howard, K.A., eds., Tectonic 

and stratigraphic studies in the eastern Great Basin Region: 

Geological Society of America Memoir 157, p. 45–59.

____1987, Implications of deformation along the east flank of the 

Charleston-Nebo thrust plate, central Utah: U.S. Geological 

Survey Professional Paper 1170–F, p. F1–F29.

____1994, The role of salt in the structural development of central 

Utah: U.S. Geological Survey Professional Paper 1528, 145 p.
12 THE CONTROVERSIAL ORIGIN OF CENTRAL UTAH’S GEOLOGIC COMPLEXITIES

WEST EAST

Arapien

Shale Kpr-TKn

KJu

Ja

Tf

Arapien Shale

Ja

Ja

KJu

WEST EAST

WEST EAST

Ja

KJu

KJu

Arapien Shale

Ja

Arapien Shale

Ja

Shale

Arapien

Ja

KJu

Arapien Shale

Ja

KJu Ja

Arapien Shale

Ja

Ja Kpr-TKn

KJu

Arapien

Shale

Ja

KJu

Kpr-TKn

Kpr-TKn

Ja

WEST EAST WEST EAST

Kpr-TKn

KJu

Arapien

Shale

Ja

Ja

Kpr-TKn Kpr-TKn

WEST EAST

Arapien

Shale

KJu

Ja

Ja

Kpr-TKn

WEST EAST

Arapien

Shale

KJu

Kpr-TKn

Tf

Ja

Arapien

Shale

Ja

KJu

Tf Ja

Tf

Kpr-TKn

WEST EAST WEST EAST

Arapien

Shale

Ja

Ja

Kpr-TKn

Tf

KJu

Tf

Tf

Arapien

Shale

Ja

KJu

Tf

Kpr-TKn

WEST EAST

WEST EAST WEST EAST WEST EAST

I II

III IV V VI

VII VIII IX X

XI XII XIII

Generalized sketch

(Red Rocks (Christianburg) area)

FIRST DIAPIRIC

EPISODE SECOND DIAPIRIC EPISODE THIRD DIAPIRIC EPISODE

Figure 8 (above and following page). Diagrammatic sketches illustrating how the sequence of intrusion, erosion, and deposition, repeated during each of the three major diapiric episodes, complexly deformed the rocks exposed in the Red Rocks area 

(G-3). Explanation and continuation of caption are on page 13.
REFERENCES CITED 13

Arapien Shale

Price River Formation and

North Horn Formation, undivided

Indianola Group, Cedar Mountain

 Formation, and Twist Gulch

 Formation, undivided

Flagstaff Limestone

Middle Jurassic

EXPLANATION

Eocene

Paleocene TERTIARY

JURASSIC

Upper

Cretaceous

Paleocene and Lower

Cretaceous

Kpr-TKn

KJu

Ja

Tf

CRETACEOUS 

Figure 8—Continued. Red Rocks area.

All sketches show only the west limb of the diapiric folds. The diapiric salt cores and the east limbs of the developing folds are east 

(right) of these exposures but are omitted for clarity.

I. Generalized sketch of Red Rocks area (G-3). View is northward.

II. Sediments of the Twist Gulch Formation (Jurassic), Cedar 

Mountain Formation (Lower Cretaceous), and the Indianola Group 

(Upper Cretaceous), all grouped and represented here by the symbol KJu, are deposited on the Arapien Shale (Ja). These undivided 

Jurassic and Cretaceous strata thin laterally as a result of the 

slowly rising salt.

First diapiric episode.

III. Intrusive stage. An upward surge of the salt diapir pushes up 

the Arapien mudstones (Ja), and they, in turn, push up and fold 

back the overlying Jurassic and Cretaceous strata (KJu).

IV. Erosional stage. Partial dissolution of the salt core causes the 

fold’s crest to collapse and founder.

V. Erosional stage—continued. Erosion of these fragmented remnants of the fold’s crest eventually produces a surface of low 

relief.

VI. Depositional stage. Younger strata, the Price River Formation 

(Kpr) (Upper Cretaceous), and the North Horn Formation (TKn) (Paleocene and Upper Cretaceous), deposited across this eroded surface, are represented by the combined symbol Kpr-TKn. The 

slowly rising salt core causes these units to thin laterally.

Second diapiric episode.

VII. Intrusive stage. The second diapiric episode begins with a renewed upward surge of the salt core. The upthrust Arapien mudstones (Ja) deform the overlying Price River and North Horn strata 

(Kpr-TKn) into a new upwarp that occupies the same site and has 

the same trend as the previous diapiric fold.

VIII. Erosional stage. Again, removal of part of the salt core causes 

the fold’s crest to founder.

IX. Erosional stage—continued. Erosion destroys these fold remnants, forming a new surface of low relief.

X. Depositional stage. Sediments of the Flagstaff Limestone (Tf) 

are deposited across this new surface. These sediments thin laterally reflecting the slow, upward movement of the salt.

Third diapiric episode.

XI. Intrusive stage. The salt diapir reactivates a third time to form a 

new upwarp that again occupies the same site and has the same 

trend as the previous two diapiric folds.

XII. Erosional stage. And again this new fold founders as part of 

the underlying salt core is removed.

XIII. Erosion stage—continued. Erosion attacks the fold’s remnants and partly destroys them, but has not, as yet, completely 

reduced the area to a surface of low relief.

Compare sketch XIII with I, generalized sketch of Red Rocks area 

(G-3).
14 THE CONTROVERSIAL ORIGIN OF CENTRAL UTAH’S GEOLOGIC COMPLEXITIES

West

East

a

b

c

d

e

f

g

A

East

West

a

b

c

d

e f

g

h

i

B

West

East

a

b

c

d

e

f

g

h

i

a b c

C

Breached

area

Figure 9. Cross sections showing fundamental differences between a typical Colorado Plateau-type monocline and a similar-appearing central Utah monocline. A, Colorado Plateau-type 

monocline. All units are conformable, and all maintain an even 

thickness. A section through this monocline is much like a section 

through an onion. B, Central Utah-type monocline. On the surface a 

central Utah-type monocline, prior to being breached, resembles 

the Colorado Plateau-type monocline—no hint is given of the underlying structural complexity. C, Central Utah-type monocline. After being breached, the monocline exposes complexly deformed 

underlying units that are considerably thinner than where these 

same units are exposed elsewhere.
REFERENCES CITED 15

EAST WEST

Tf

Kpr-TKn

KJu KJu

EAST WEST

Arapien Shale

Ja South wall—Red Canyon, Valley Mountains

EAST WEST

KJu

Ja KJu

Arapien Shale

EAST WEST

Ja

KJu

Arapien Shale

EAST WEST

Kpr-TKn

Ja

Arapien Shale

KJu

EAST WEST

KJu

Ja

Kpr-TKn

Kpr-TKn

Arapien

Shale

Ja

EAST WEST

Kpr-TKn

KJu

Arapien 

Shale

Ja

EAST WEST

KJu

Ja

Tf

Kpr-TKn

Arapien

Shale

EAST WEST

Tf

Kpr-TKn

KJu

Arapien

Shale

Ja

EAST WEST

Tf

Kpr-TKn

KJu

THIRD DIAPIRIC

EPISODE

IX X

VI VII VIII

SECOND DIAPIRIC

EPSODE

FIRST DIAPIRIC

EPISODE

III IV V

I II

Figure 10 (above and following page). Red Canyon area, Valley Mountains. Explanation and continuation of caption are on page 16.
16 THE CONTROVERSIAL ORIGIN OF CENTRAL UTAH’S GEOLOGIC COMPLEXITIES

Arapien Shale

Price River Formation and

North Horn Formation

Indianola Group, Cedar Mountain

 Formation, and Twist Gulch

 Formation, undivided

Flagstaff Limestone

Middle Jurassic

EXPLANATION

Eocene

Paleocene TERTIARY

JURASSIC

Upper

Cretaceous

Paleocene and Lower

Cretaceous

Kpr-TKn

KJu

Ja

Tf

CRETACEOUS 

Figure 10—Continued. Red Canyon area, Valley Mountains.

I. Diagrammatic sketch of the south wall of Red Canyon in the Valley Mountains. View is southward. All sketches are of the west 

flanks of the diapiric folds. The causative salt diapir, east (left) of 

the area shown, is not exposed.

II. Sedimentary units of the Twist Gulch Formation (Jurassic), Cedar Mountain Formation (Lower Cretaceous), and the Indianola 

Group (Upper Cretaceous) are all here grouped under the symbol 

KJu. These units, deposited on the Arapien Shale, thin laterally 

eastward (left) reflecting the slow, upward movement of a salt diapir within the Arapien Shale.

First diapiric episode.

III. An upward surge of the salt diapir forces up the Arapien mudstones (Ja), and they, in turn, push up and deform the Jurassic and 

Cretaceous country rocks (KJu).

IV. Dissolution of part of the salt core causes the fold to founder, 

much as shown in figure 3B. Erosion removes the foundered 

blocks and cuts a surface of low relief across the upturned Jurassic and Cretaceous country rocks (KJu).

V. Younger sediments of the Price River Formation (Kpr) and the 

North Horn Formation (TKn), deposited across the erosional surface, thin eastward (left) in response to the slowly rising salt diapir.

Second diapiric episode.

VI. A renewed upward surge of the salt diapir forms a new diapiric 

fold.

VII. And again, dissolution of part of the salt core causes the fold to 

fail. Erosion removes the foundered blocks and then cuts a new 

surface of low relief across the Price River and North Horn (KprTKn) country rocks.

VIII. Sediments of the Flagstaff Limestone (Tf) are deposited across 

this newly formed surface.

Third diapiric episode.

IX. What happened next is uncertain; two alternatives are possible. 

One alternative suggests that the salt surged upward once again 

to form a new diapiric fold. Subsequently, this fold failed and the 

flanks of the fold subsided to form paired, facing monoclines (much 

as shown in fig. 3C).

An alternative interpretation (shown here) is that the salt core remained quiescent; in essence, a new diapiric fold was not formed. 

Continued dissolution of the salt core removed support from the 

flanks of the fold, which then subsided to form paired, facing monoclines. Only the western monocline is shown here.

X. Erosion removed part of the downwarped Flagstaff Limestone 

(Tf), breaching the monocline and exposing the compexly deformed Price River (Kpr), North Horn (TKn), and the underlying Jurassic and Cretaceous units (KJu). 

Compare sketch X with sketch I.

The end result is upturned older beds (units of Jurassic, Cretaceous, and Tertiary age (KJu and Kpr-TKn)), overlain by downturned younger ones (the Flagstaff Limestone (Tf))—in my view the 

fundamental structural pattern of central Utah.